In a device where power dissipation must be minimized in a diode, a circuit can be constructed such that the average power dissipation in the circuit is significantly reduced when compared to a traditional PN junction diode. This is especially valuable in a sealed enclosure or small space where high power dissipation can cause significant temperature rise and limitation of the maximum current through the device. A common example of this is in the PV junction box where diodes are used extensively to bypass low performing sections of solar cells, allowing the other cells to maximize their power output. Because of the excessive power dissipation in some traditional PN junction diodes, the box can get so hot that the devices inside fail or have a reduced operating life expectancy.
Some methods already exist that utilize a boost driven from the voltage drop across the body diode of a FET. These parts are complicated, expensive and require ultra-low input voltage boost circuits to operate. Additionally, they are limited to the choice of MOSFET picked and integrated into the component by the manufacturer. Building a circuit with discrete component allows the designer to choose a MOSFET that is optimal for the application.
The solution according to the present disclosure is implemented with a switching circuit that switches between a low-impedance “forward conducting bypass” state and a charging state. Ideally the duty cycle is as high as possible, but is practically limited by the quiescent current of the circuit and switching speed. During the charging state, the low-impedance bypass path is shut-off and there is a higher voltage drop across a zener diode that charges the circuit. Once the circuit is fully charged, it switches back into the low impedance “forward conducting” state. The circuit will remain in this “forward conduction” state until the charge has depleted to a level low-enough that the MOSFETs are no longer efficient in providing a low-impedance path. The cycle repeats by cycling between these two states. During the charging state, there will be high power dissipation so it must be kept to a minimum amount of time.